Find out the best antibiotic treatment for preventing bacterial infections and PCP in HIV-infected children. We will compare two antibiotic treatments. The two treatments are the combination of azithromycin and atovaquone against the single antibiotic trimethoprim-sulfamethoxazole (TMP/SMX). We will also find out if the two treatments are safe and easily tolerated. Nationwide there will be a total of 690 children in the study. At Vanderbilt there will be about 4 children in the study. All children will be taking the study treatment of approximately 2-3 yrs. The treatment of either atovaquone and azithromycin OR trimethoprim-sulfamethoxazole (TMP/SMX) alone will be decided randomly.